The present invention relates to a process for the preparation of primary aliphatic polyamines from the corresponding aminoalcohols and/or polyalcohols. The polyamines which can be prepared according to the invention have the general formula 
In this formula, R1 and R2 independently of one another are hydrogen, methyl, ethyl or aminomethyl.
It is, known that some primary diamines can be prepared from the corresponding alcohols or aminoalcohols. The industrially most important process of this type is the preparation of 1,2-ethanediamine (ethylenediamine) from ethanolamine. However, there are only a few processes for the analogous preparation of aliphatic polyamines of the formula I, whose efficiency is moreover low. Thus, instead, starting compounds which are complicated to prepare or complex preparation processes are chosen and usually only low yields are obtained.
U.S. Pat. No. 4,123,462 discloses a method for the preparation of amines using a nickel/rhenium catalyst. The examples given indicate the amination of 1,3-propanediol with a conversion of 45%. Details of the product yields or selectivities are not mentioned.
In U.S. Pat. No. 4,158,017, hydroxypivalaldehyde is employed as a starting compound in order to obtain the corresponding diamine (2,2-dimethyl-1,3-propane-diamine, xe2x80x9cneopentyldiaminexe2x80x9d). Hydroxypivalaldehyde is a starting compound which is complicated to prepare, whose amination needs a number of reaction stages. Because of this, this process is not very economical.
According to U.S. Pat. No. 5,099,070, it is essential for the preparation of neopentyldiamine by reaction of neopentanolamine (3-amino-2,2-dimethyl-1-propanol) with ammonia in the presence of hydrogen on a nickel catalyst that the starting material is free of neopentyl glycol in order to avoid, possible side reactions of the diol such as hydrogenolysis.
In U.S. Pat. No. 5,288,911, a catalyst of cobalt and iron is used in order preferably to produce (x,(i)-aminoalcohols from (x,(i)-alkanediols. From the examples disclosed, it is evident that the diamine is only obtained as a byproduct. The process shown is (therefore not suitable for the industrial preparation of the diamine.
The prior art does not disclose any process by means of which primary aliphatic polyamines having more than two terminal amino groups can be obtained directly from the corresponding alcohol of the formula I. The industrial preparation of compounds of this product class, e.g. 2-aminomethyl-2-methyl-1,3-propanediamine (xe2x80x9c1,1,1-tris(aminomethyl)ethanexe2x80x9d), 2-aminomethyl-2-ethyl-1,3-propanediamine (xe2x80x9c1,1,1-tris(aminomethyl) propanexe2x80x9d) or 2,2-bis(aminomethyl)-1,3-propanediamine (xe2x80x9cpentaerythrityltetraminexe2x80x9d) from the corresponding easily accessible polyalcohols, however, is particularly attractive. A known multi-stage synthesis (E. B. Fleischer et al., J. Org. Chem. 1971, 36, 3042) requires the azide as an intermediate. Azides are prone to explosive decomposition, which does not make them very suitable for industrial processes.
The object of the present invention was therefore to make available a process suited to being carried out on an industrial scale, which in one stage yields primary aliphatic polyamines from the corresponding polyols.
According to the invention, this object is achieved by the process according to Patent claim 1.
Starting from primary aliphatic polyalcohols of the general formula 
in which R1xe2x80x2 has the meaning mentioned above for R1 or, if R1 is aminomethyl, R1xe2x80x2 can also be hydroxymethyl, and R2xe2x80x2 has the meaning mentioned above for R2 or, if R2 is aminomethyl, R2xe2x80x2 can also be hydroxymethyl, it was found that by reaction with ammonia in the presence of hydrogen the corresponding primary polyamines can be obtained in single-stage process if a catalyst containing nickel and/or cobalt is employed and the ammonia is in the supercritical state, i.e. under a pressure of more than 113 bar and at a temperature of more than 133xc2x0 C., and the quantitative ratio is 1-300 mol of ammonia and 0.01-20 mol of hydrogen to 1 equivalent (eq.) of polyalcohol II.
The pressure is preferably 115-300 bar and the temperature 150-300xc2x0 C.
Pressures of 120-200 bar and temperatures of 160-250xc2x0 C. are particularly preferred.
The quantitative ratio is preferably 10-100 mol, particularly preferably 40-90 mol, of ammonia and 2-10 mol, of hydrogen to 1 equivalent (eq.)of polyalcohol.
The metal fraction of the catalyst preferably has a content of 5-95 percent by weight nickel and/or cobalt.
Catalysts are particularly preferred which additionally contain 1-60 percent by weight of Fe and/or La as a further metal.
It has moreover been shown that the catalyst should not be too basic or too acidic.
The catalysts employable according to the invention can be prepared, for example, by precipitating the hydroxides, hydrated oxides and/or hydroxycarbonates of the active metals at a pH of 5-9, and drying and calcining them at 200-500xc2x0 C. in an oxidizing atmosphere.
A certain number and concentration of basic and acidic centres on the catalyst surface are advantageous for the amination of the alcohols, as the adsorption and activation of ammonia and of the aminoalcohol, which recurs as an intermediate require these centres. Strongly basic and strongly acidic centres on the catalyst surface, however, should be avoided. Such centres are induced, for example, by reagents having strongly basic ions such as, for example, sodium, potassium, calcium, barium or strongly acidic ions such as, for example, phosphate, hydrogenphosphate. In this context, the basicity or acidity relates to the action on the solids surface and not to the customarily considered properties in solution. It was found that centres of this type have an adverse effect on the selectivity of the reaction to give the desired products, and base- or acid-catalysed side reactions such as fragmentation, cyclization and oligomerization are favoured. One possibility of influencing the acidic and basic properties of the catalyst is the checking of the pH during the precipitation of the catalyst. The precipitation should therefore be carried out at a pH of 5-9. Furthermore, it is advantageous to wash the precipitate carefully.
The precipitation can be carried out, for example, by addition of a base to a solution of the acetates, nitrates or halides of the metal component(s). Preferred bases for this are ammonium carbonate and carbamate or ammonia. Drying is preferably carried out at temperatures tip to 150xc2x0 C., if appropriate in vacuo.
The catalyst is preferably calcined at 300-500xc2x0 C. in an oxidizing atmosphere.
For the catalyst, a support such as silica, kieselguhr, alumina or graphite can be used. For this purpose, the precipitation can be carried out in the presence of the support.
Before use, the catalyst is advantageously activated at temperatures of 200 to 400xc2x0 C. by reducing gases such as, for example, hydrogen.
The process according to the invention can be carried out with unbranched and branched polyalcohols II. 1,3-Propanediol 2-methyl-1,3-propanediol, 2,2xe2x80x2-dimethyl-1,3-propanediol, 1,1,1-tris(hydroxymethyl)-ethane and pentaerythritol are particularly preferred.
The process according to the invention can be carried out batchwise or continuously; the continuous procedure is preferred.
The contact time (defined as the quotient of catalyst mass [g] and supplied molar flow [mol/s] of the reaction components) when carrying out the process continuously is preferably 10,000 gxc2x7s/mol. to 100,000 gxc2x7s/mol.
In the continuous procedure, the unreacted polyalcohol and/or the unreacted ammonia is preferably recycled. By this means, even with (after a single passage) a relatively low conversion a satisfactory to good product yield can be achieved.
The ammonia can be supplied to the reaction vessel as a gas, but preferably as a liquid; the supercritical state can then be achieved starting from the gas or the liquid phase. In the case of solid starting materials, the use of liquid ammonia has the advantage that these can already be dissolved before achieving the supercritical state and the reaction mixture is thus present from the start as a homogeneous phase. The reaction mixture is advantageously cooled after the reaction, e.g. by adiabatic expansion, and the ammonia is separated off and optionally fed back into the process.
The aliphatic primary polyamines of the formula I which can be prepared by the process according to the invention can be employed, for example, for polyurethane preparation, in particular as crosslinkers and/or catalysts having a low migration tendency.